This invention relates to a control system of an injection molding machine and a temperature control device utilized thereby.
As is well known in the art, a conventional molding machine comprises a pair of metal molds, a mechanism for opening, closing and clamping the metal molds, and an injection mechanism including a heater for melting a plastic material and an injection piston or screw for injecting molten plastic into closed metal molds. The clamping mechanism comprises a product take-out device designed to change the method of taking out the product in accordance with the size and configuration thereof and to change the injection stroke. The hopper, the product take-out device, etc. are hereinafter termed a peripheral apparatus.
It has been desired to automate the control system of the injection molding machine described above. However, it is difficult to design the control system to have all control performances for the injection molding machine (main body) itself and for the peripheral apparatus. For this reason, respective peripheral apparatus are designed to have necessary control performances commensurate with molding conditions.
More particularly, for a hopper, one of the peripheral apparatus, it is necessary to switch the control performances therefore for different raw material plastics, and for a product take-out device it is necessary to design the control system such that exchange of a chuck and variation of the injection stroke can be automatically made in accordance with the molded product.
Certain specifications of the injection molding machine do not require to attach some sort of peripheral apparatus. Moreover, the operation mode and the connection of the peripheral apparatus are not equal for products of different makers.
For this reason, unless the capacity of memory means of the main body of the injection molding machine is increased, it is impossible to store all molding condition set data for all peripheral apparatuses.
Even if the memory capacity were increased, each time a machine maker incorporates a different peripheral apparatus it is necessary to change the entire program of the memory means.
For this reason, the control systems for respective peripheral apparatus have been constructed to have different control performances commensurate with the molding conditions. In order to completely automate the control system of an injection molding machine incorporated with peripheral apparatus requiring various control performances commensurate with different molding conditions, it has been the greatest problem how to construct the overall control system for the entire injection molding equipment.
Among the peripheral apparatus is also included a temperature control device for controlling the temperature of the plastic heating cylinder. In recent years, a temperature control device has been used capable of preventing breakage and excessive temperature rise of the heating cylinder caused by the overheating of an electric heater.
Prevention of breakage caused by the overheating of the heater can be accomplished by detecting breakage of a thermostat, but where the thermostat is not satisfactorily inserted into a portion whose temperature is to be detected, as the fault is not caused by the breakage of the thermostat, such fault cannot be detected with a prior art device which detects the breakage of the electric heater. As a consequence, the heater continues to operate until it is broken by overheating. Furthermore, the overheating of the heating cylinder cannot be confirmed unless the operator observes whether the needle of the temperature control device reaches a set vale to ON-OFF control the heater.